The field of the invention relates generally to electric motor control systems, and more particularly, to moisture penetration protection for electric motor control systems used in high-moisture applications.
Electric motors are being utilized in a plurality of different heating, ventilation, and air conditioning (HVAC) applications (furnaces, heat pumps and air conditioners) with acceptable records of reliability. Although the reliability of electric motors has steadily increased through the years, there is an industry need for a moisture resistant electric motor to meet an increasing demand for longer warranties (e.g., from 1 year to 5-10 years). Moisture penetration is a leading cause of failures in electronic components of motor control systems, particularly in air conditioners and heat pumps where high-level humidity level typically occurs. Connectivity (e.g., integrity of signal connectors) is another leading cause of failures.
Present packaging processes in at least some known motor control systems include printed circuit board (PCB) mounted electronic components and cable connections for power and signal lines. Surface-mount thick film resistors used in the motor control systems are very sensitive to moisture penetration. When moisture penetrates the hardware electronics, silver migration at resistor terminals occurs and causes a resistance drop, resulting in a short circuit or disconnection. The connectors used for the power lines and the signal lines also provide a moisture penetration path, which impacts the overall moisture level of motor drive electronics inside the enclosure. In general, power lines of the motor control system input and connections carry higher current levels when the motor is running, so the resistive loss produced by the cable itself may reduce the surrounding moisture level. However, signal connections between the electric motor and the HVAC system controller typically carry very low current, so it cannot reduce the level of surrounding moisture. As a result, moisture penetrates the low power signal-level circuit, which includes numerous moisture sensitive components, and eventually results in a failure. As such, the known PCB-based packaging techniques do not provide a solution to moisture ingress over the desired warranty time, which causes field failures and additional expenses for consumers and motor suppliers.